"I've only been wrong like this twice in my life. And that's a
career that spans since 1986, 30 years," he said. "I've done this
for a long time. I've polled every statewide election in Michigan
going back 30 years ... I don't like to get it wrong, but
I'm not alone."

He added: "I have never seen anything like
this."

Mitchell's poll had Clinton winning by 27 points over Sanders of
Vermont. Other polls were also significantly off the mark.

The
past 15 polls listed for Michigan on RealClearPolitics had
Clinton winning the state by at least 10 points. The three most
recent found her leading by an average of more than 20
points. Another recent poll from Mitchell had her winning by
a whopping 37 points.

At the same time, many of the same polls that were so far off
about the Democratic race were spot on for the GOP results.
Mitchell's most recent poll for the GOP had party frontrunner
Donald Trump beating Ohio Gov. John Kasich by a spread of 41% to
23%. Trump ended up finishing with 36.5%, with Texas Sen. Ted
Cruz barely edging out a second-place finish
over Kasich.

"As I told my client, I'm in some pretty good company," Mitchell
said before listing other major polling institutions that missed
the mark with the Democratic primary. "Everybody else who polled
it, nobody had it right, nobody had it within double digits.
We're pleased with our Republican numbers."

He said that his team is still looking into what exactly they
missed. But he and other pollsters said that it's likely a
combination of small factors that led to the shocking final
result.

First, he said that his reliance on landlines, rather than
cellphones, may have played a role in the distorted numbers.
But he added that it doesn't tell the full story.

He said:

Because we thought 82% or 86% of voters were going to be over the
age of 50, we thought we could use just landlines. But some of
the polling [conducted by others] was also done with cellphones.
There were a lot of companies that were doing both and came up
with the same bad results. Something happened in terms of the
voter turnout that we did not anticipate or build into our
model.

AP
Photo/Alan Diaz

Tom Jensen, the director of Public Policy Polling (PPP), told
Business Insider in an email that the landline aspect did play a
big part in the inaccuracy.

"There's a huge divide in the Dem race between people who
have landlines and people who don't, and your polls are going to
massively overstate Clinton's support if you don't contact the
people without them," he said.

PPP had found Clinton up 10 points in a mid-February
poll.

Young voters turned out in much higher numbers than anticipated.
Exit polls from NBC News showed that 37% of voters were between
18 and 39. And 21% overall were between 18 and 29. Mitchell said
that he had projected only 8.7% of the total vote would come
from those between 18 and 39. His survey also had Sanders
winning that age group by a 2-to-1 split. Exit
polls showed that he won the age group by about 4-to-1.

Mitchell said that the numbers regarding Clinton's
African-American support were expected to be far stronger, as
well. He projected a 40- to 50-point margin in the
results, but she won instead by about a 2-to-1 gap, far less than
in other states.

"We're going to figure out what went wrong and we're going to
figure out how to fix it," he said.

Another reason floated for the polling
discrepancy: Michigan's status as an open primary, in which
registered Democrats and Republicans can vote in the other
party's primary. Democrats could theoretically have voted
for a Republican in hopes of upsetting Trump or ensuring his win,
rather than vote for Clinton if they thought it was a done deal.

Reporters found some anecdotal evidence of this occurring:

I just keep meeting Dems in MI who say Hillary has the primary locked, so they cast anti-Trump votes for Kasich.

Exit polls also provided this theory some weight. According to
those exit surveys, 7% of Michigan Republican primary voters
identified as Democrats. Just 3% of Democratic primary voters
identified themselves as Republicans.

"You know, I think a lot of inside-baseball people do think like
that. How large the number is, I don't know," Mitchell said. "But
obviously if it was only 20,000 to 30,000 that made the
difference between Hillary winning and losing, it could've played
a factor."

He added that he did not see much crossover in his polling.

Jensen agreed that the crossover factor may have played
a role in the disparity between the polls and the results. He
said that, because of the "overwhelming media narrative based on
the polls that Michigan was a blowout for Clinton," Democrats
found it worthwhile to vote Republican.

He cited the Ann Arbor precinct where he grew up as an example.
That precinct provided Mitt Romney with 175 total votes in the
2012 general election. On Tuesday night, 250 people cast ballots
in the GOP primary, with about two-thirds of the vote going
to Kasich.

"That's obviously a very micro level observation but kind of
remarkable to have 40% more people vote in a GOP primary than
voted GOP in the last general," he said. "And I think it was much
more likely to be complacent Hillary voters who did that kind of
thing."

Upon finding out that the results would be far closer than anyone
anticipated, Mitchell said that he still believed Clinton would
pull out a close win once all of the votes in places like
Detroit and Grand Rapids were tabulated.

Once he knew that wouldn't be true, he thought to himself:
"Everybody has gotten this thing wrong."